In control systems including a control unit and a plurality of output units and input units or a plurality of controlled devices, so-called wiring saving of reducing the number of wires has been widely performed. As a general technique for wiring saving, a technique of connecting a master station with a function of performing conversion between a parallel signal and a serial signal and a plurality of slave stations with a control unit and a plurality of output units and input units or a plurality of controlled devices, respectively, and performing data transfer between the master station and the plurality of slave stations via a common data signal line using a serial signal, instead of a parallel connection of connecting each of signal lines extending from a plurality of output units and input units or a plurality of controlled devices directly to a control unit has been widely employed.
In the case in which wiring saving is implemented, when it is difficult for a control unit side to identify a failure of an output unit, an input unit, or a controlled device in a state in which a number of slave stations are connected, it is necessary to check the output unit, the input unit, or the controlled device far away from the control unit, and thus it requires many man-hours to identify a failure spot.
In this regard, the present applicant has considered applying a remote wiring check system disclosed in JP 2011-114449 A as a system in which a disconnection failure of a slave station and an input unit or an output unit is identified at a control unit side. In this remote wiring check system, in a control/monitoring signal transmission system including a single control unit and a plurality of controlled devices, a management data region including connection data indicating a wiring state which is different from a control/monitoring data region including control data (output data) and monitoring data (input data) which are bidirectionally and simultaneously transmitted between a master station and a slave station connected via a wiring-saved data signal line is provided. In the connection data, short circuit information, disconnection information, and normality information are identified. Thus, it is possible to easily check the wiring connection state of the slave station, between the slave station and the input unit, or between the slave station and the output unit without reducing input data (monitoring data) capacity of a signal.
Further, JP 2006-331449 A discloses a slave (slave station) having a function of acquiring start time information when an ON state or an OFF state of an OUT terminal connected with an output device (output unit) has changed by OUT data received through serial communication with a master unit (master station), a function of acquiring stop time information when an ON state or an OFF state of an IN terminal connected with an input device (input unit) has changed, and a calculation function of calculating an operation period of time of the output device based on the start time information and the stop time information. According to this slave (slave station), it is possible to determine whether the output device or the input device is in the normal state, whether a replacement time has approached, or the like by obtaining the operation period of time of the output device or the input device and comparing the obtained operation period of time with setting information used for identifying a normal range of the output device or the input device.